[mlmilleratmit]

Nice work -- that's a hard problem. I've felt some of this pain as I helped Cloudant customers make hot migrations from mongo to into Cloudant. Your first two figures make it clear just how challenging hot-replications are (especially master-master), not to mention handling failure scenarios. For all of the great things about Mongo, there's something very awesome to be said for CouchDB's MVCC replication model. Glad to see that you're open sourcing those tools. Maybe they could be extended to make a MongoDB <==> CouchDB replicator.